I just had a similar question and wrote a test case, and the first answer was similar to yours, however we both did not consider that modern JS-engines are very capable at eliminating code that is irrelevant for the result of a function.
That means that your test-case is showing you misleading results, because the JS-engine was able to remove your test-case entirely, therefore you measured how fast the engine can run an empty loop.
I wrote a new test-case that makes sure that the browser has no chance to eliminate the code, and the results shows that maps are almost twice as fast as associate objects:
https://jsperf.com/map-vs-object-vs-frozen
Please note that this test does not include the cost to actually initialize the Map-object. In reality it is therefore most likely faster to use local objects for small snippets of code, where actual Maps are only faster in a case where you store larger amounts of data in a global context.
It is also interesting to see, that the browser realizes that there are no write-operations on the object and therefore ignores all update checks it would otherwise have to do. Therefore the frozen performance is actually slower, while one would expect it to be faster.